1. Field of the Invention
The present disclosure relates to a digital hologram display device for reproducing/replaying digital hologram video data for playing three dimensional video images. Particularly, the present disclosure relates to a digital hologram display device in which the 0th diffraction component is removed for optimizing the reproduction and replay of the three-dimensional hologram video data.
2. Discussion of the Related Art
Recently, technologies and researches for making and reproducing the 3D (Three Dimensional) images/videos are actively being developed. As the media relating to the 3D image/video is a new concept for virtual reality, it can improve the visual information better, and it will lead to the next generation display devices. The conventional 2D image system merely suggests the image and video data to be projected into plan view, but the 3D image system can provide the full real image data to the viewer. So, the 3D image/video technologies are the True image/video technologies.
Typically there are three methods for reproducing 3D images/videos: the stereoscopy method, the holography method and the integral imaging method. Among them, the holography method is the most ideal method because it has an excellent visual autostereoscopic property without any fatigue of an observer.
To produce a recording of the phase of the light wave at each point in an image, holography uses a reference beam which is combined with the light from the scene or object (the object beam). If these two beams are coherent, optical interference between the reference beam and the object beam, due to the superposition of the light waves, produces a series of intensity fringes that can be recorded on standard photographic film. These fringes form a type of diffraction grating on the film, which is called the hologram. The central goal of holography is that when the recorded gratng is later illuminated by a substitute reference beam, the original object beam is reconstructed (or reproduced), producing a 3D image/video.
There is a new development of the computer-generated holography (or CGH) that is the method of digitally generating holographic interference patterns. A holographic image can be generated, e.g., by digitally computing a holographic interference pattern and printing it onto a mask or film for subsequent illumination by a suitable coherent light source. The holographic image can be brought to life by a holographic 3D display, bypassing the requirement to fabricate a “hardcopy” of the holographic interference pattern each time.
Computer-generated holograms have the advantage that the objects which one wants to show do not have to possess any physical reality at all. If holographic data of existing objects is generated optically, but digitally recorded and processed, and brought to display subsequently, this is termed CGH as well. For example, a holographic interference pattern is generated by a computer system and the generated pattern is sent to a spatial light modulator such as LCSML (Liquid Crystal Spatial Light Modulator), then the 3D image/video corresponding to the holographic interference pattern is reconstructed/reproduced by illuminating a reference beam to the spatial light modulator. FIG. 1 is a structural drawing illustrating a digital holography image/video display device using a computer-generated holography according to the related art.
Referring to FIG. 1, a computer 10 generates a holographic interference pattern of an image/video data to be displayed. The generated holographic interference pattern is sent to a SLM (Spatial Light Modulator) 20. The SLM 20, as a transmittive liquid crystal display device, can represent the holographic interference pattern. At one side of the SLM 20, a laser source 30 for generating a reference beam is located. In order to collimate a reference beam 90 from the laser source 30 onto the whole surface of the SLM 20, an expander 40 and a lens system 50 can be disposed, sequentially. The reference beam 90 out from the laser source 30 is illuminated to one side of the SLM 20 passing through the expander 40 and the lens system 50. As the SLM 20 is a transmittive liquid crystal display device, a 3D image/video 80 corresponding to the holography interference pattern will be reconstructed/reproduced at the other side of the SLM 20.
At this time, there are some components of the reference beam 90 which are not diffracted by the holographic interference pattern but just passing through the holographic interference pattern. These components are called the “DC component” or the “0th diffraction component.” The 0th diffraction component passing through the holographic interference pattern is superimposed with the reproduced images and causes the deteriorated image/video quality. Up to now, there are some researches for eliminating the 0th diffraction component in the digital holography.
For example, there is one method in which the 0th diffraction component is reduced by diffusing it using a concaved lens in front of the SLM (see OpticsInfoBase, July 2009, “Experimental modules covering imaging, diffraction, Fourier optics and polarization based on a liquid-crystal cell SLM”). However, the reproduced image may be smaller than the original image. Another method is where the intensity of the 0th diffraction component is lowered by using a polarizer in front of the SLM (see Otics Express, September 2008, “Hologram optimization for SLM-based reconstruction with regard to polarization effects”). In this case, the intensity of the reproduced image is also lowered. For still another method, the 0th diffraction component can be eliminated by mechanical methods. However, in these cases, the reproduced image can be damaged or these methods cannot be available to large 3D images at all.